This invention relates to a method of performing maintenance work on an unmanned offshore platform using a maintenance crew and also to the unmanned offshore platform itself. The term xe2x80x9ccrewxe2x80x9d as used herein means one or more crew members though normally the crew will contain a plurality of members.
Offshore platforms are either manned or (normally) unmanned. In the case of unmanned platforms, these are typically used where the well drilling operations have been completed and the oil or natural gas to be recovered is in production. However, such unmanned offshore platforms require periodic maintenance, for which purpose a maintenance crew has to visit the platform to carry out the necessary maintenance work. Sea access to offshore platforms can be limited by adverse weather conditions in many parts of the world. One such location of particular commercial importance is the North Sea. In such areas, helicopters have conventionally been used to transfer maintenance crews between their operating base, for example at an onshore location or at another offshore platform, and the unmanned offshore platform. In order that a helicopter can land on an offshore platform, a xe2x80x9chelideckxe2x80x9d has to be provided on top of the platform superstructure, on which the helicopter lands. The provision of such a deck adds considerably to the cost of the platform. Furthermore, in particularly adverse weather conditions it is not safe for the helicopter to land and take the crew back to base as soon as the maintenance work has been completed. Under those circumstances, the maintenance crew have to stay on board the platform until the weather settles down again. This can take a long time. Therefore, unmanned offshore platforms are provided with crew accommodation, which further adds to the cost of the platform. For all these reasons, a need exists for a low cost unmanned offshore platform, and also a system and method for safely and easily transporting maintenance crew between their base location and the unmanned offshore platform, even under adverse weather conditions.
Another problem arising with an unmanned offshore platform is that certain electrically or hydraulically driven services need to be operational, to enable the maintenance operations to be carried out. These services are not, however, needed most of the time, when the maintenance crew are not on the platform. Furthermore, the power consumption of such services is significantly larger than for the basic services that need to remain operational at all times, such as navigational aids and general instrumentation on the platform. Therefore, energy generators, such as electrical power generators or engine-driven hydraulic motors, have to be especially provided on board the platform for use when maintenance is to be carried out. This also adds to the cost of the platform where such generators or motors are permanently installed on the platform. If instead they are transported in the support craft, this is inconvenient for the crew, particularly when transporting such equipment from the craft to the platform.
Reference is made to the British patent application No. 99 03325.0 in the name of Caley Ocean Systems Ltd., filed Feb. 15, 1999, which discloses a hoisting apparatus for launch and recovery of a support craft from a manned or unmanned offshore platform, and a method of using the same in conjunction with an offshore platform and support craft for performing various functions, one of which can be maintenance, e.g. repair, work.
According to the present invention from one aspect, there is provided a system for use in performing maintenance work on an unmanned offshore platform, comprising a sea-going support craft for transporting a maintenance crew to the platform for performing maintenance work on the platform, a power generator on the craft, at least one operating device on the platform, a line connected to said operating device, and connector means for connecting the line to the power generator such that the latter can supply power to said operating device.
With this arrangement, the power supply needs of the platform during maintenance are met by the power generator on board the support craft. The need for power generation on the platform or transportation of power generation to the platform and transfer to its superstructure is avoided.
Preferably, the or one of the operating devices is a hoisting apparatus for raising the support craft to an elevated position, enabling the crew to transfer from the craft to the platform superstructure. Therefore, a simple, safe and reliable transfer of maintenance personnel to the unmanned platform can be achieved, even in adverse weather conditions. Furthermore, the need for a helicopter landing is avoided and the support craft held in its elevated position can serve to provide temporary crew quarters. Therefore, the cost of the unmanned platform is significantly lower than when helicopter landing facilities and crew accommodation have to be provided.
Conveniently, means, remotely operable from the craft, are provided on the platform for lowering the line to the craft.
The power generator is preferably an electrical power generator. However, it could alternatively be a hydraulic power generator.
Suitably, the electrical power generator can be arranged to be driven by the marine engine of said vessel, said engine being adapted to run when the support craft is held in its elevated position. Alternatively, it can be arranged to run independently of the marine engine of said craft, the generator being adapted to run when the support craft is held in its elevated position.
According to the invention from a second aspect, there is provided an unmanned offshore platform having a low maintenance self-sustainable power supply, a first electrical circuit including at least one first electrical device arranged to be powered by the power supply, and a second electrical circuit including at least one second electrical device, said second electrical circuit having no permanent power source on board the platform but having an electrical connection means for connecting to an external source of power on a sea-going support vessel for transporting maintenance crew to the platform. xe2x80x9cSelf-sustainablexe2x80x9d as used throughout this specification denotes that the power supply ordinarily supplies power continuously despite the offshore platform being unmanned. This can be achieved by using a renewable energy source, such as solar, wind or wave powered, or an energy source that derives power from the well(s) from which the offshore platform is a production platform, or from neighbouring wells.
With this arrangement, the essential functional requirements of the platform, such as provided by the platform instrumentation and navigational aids and/or the ability to lower an umbilical line from the platform to the support craft, can be maintained at all times and functions needed only when maintenance crew periodically visit the platform, which generally have larger power requirements, are maintained by the generator on the support craft.
The power supply may comprise a self-sustainable energy source and a battery arranged to be recharged by the self-sustainable energy source. Suitably, the unmanned offshore platform includes two or more self-sustainable energy sources to provide alternative sources of energy. One, or more, of the self-sustainable energy sources may be a thermal electric generator arranged to burn gas from a gas well, for which said platform is a production platform. Alternatively, the, or one of the, self-sustainable energy sources is a photo-voltaic solar source.
In one preferred arrangement, the second electrical circuit is connected to the first electrical circuit through one-way converter means, to enable the external source of power on the support craft to re-charge the battery and energise the first electrical circuit when said external source of power is connected to the second electrical circuit.
The first electrical device(s) may comprise at least one of (i) a motor for driving a hydraulic package, (ii) a motor for operating an umbilical winch for lowering to the support craft an umbilical power line connected between said second electrical circuit and said connection means, (iii) instrumentation and (iv) navigational aids. The umbilical winch motor is preferably operable by remote control from the support vessel or from a host platform. The second electrical device(s) may comprise at least one of (i) a winch motor for raising and lowering the support vessel between sea level and an elevated position alongside the platform superstructure (ii) an electrically powered crane on the platform and (iii) an electrical distribution board.
It is advantageous for the unmanned offshore platform to include a support vessel raising and lowering apparatus on the platform superstructure, comprising a primary load-bearing line for connection to the craft, means operable for raising and lowering the primary line, a load member, a plurality of secondary lines connected to the load member, docking means on the load member for engagement with corresponding docking means on the support vessel, and means operable for raising and lowering the secondary lines independently of the load bearing line, said load member acting as a guide for the primary line. This arrangement is effective for easy and reliable docking with the support craft even in stormy weather conditions.
According to the invention from a third aspect, there is provided a system for use in performing maintenance work on an unmanned offshore platform, comprising a sea-going support craft for transporting a maintenance crew to the platform, an operating device on the platform, a hoisting apparatus on the platform which can be coupled to said support craft and is operable therefrom to raise the support craft from the sea to an elevated position alongside the platform superstructure, means on the platform remotely operable from the craft for lowering a line, connected to said operating device and said hoisting apparatus, to the craft before it is raised from the sea, and connector means for connecting the lowered line to the craft such that the latter can supply power to said operating device and said hoisting apparatus.
In this way, the power supply requirements of both the operating device and the hoisting apparatus are jointly met by supplying power from the support craft.
According to the invention from a fourth aspect, there is provided a method of performing maintenance work on an unmanned offshore platform using a maintenance crew, wherein the crew:
(i) are transported in a sea-going support craft to the platform;
(ii) connect a hydraulic pressure source on the craft to a hydraulic hoisting apparatus on the offshore platform;
(iii) operate the hoisting apparatus from the craft to raise the support craft from the sea to an elevated position;
(iv) transfer from the craft in elevated position to the platform superstructure; and
(v) perform said maintenance work.
Conveniently after said maintenance work has been completed, the crew transfer back to the support craft in the elevated position, operate the hoisting apparatus to lower the craft down to the sea, and are transported away from the offshore platform in the vessel.
According to the invention from yet another aspect, there is provided a system for use in performing maintenance work on an unmanned offshore platform, comprising a sea-going support craft for transporting a maintenance crew to the platform, a hydraulic pressure source on the support craft, a hydraulic hoisting apparatus on the platform which can be coupled to said support craft and is operable therefrom to raise the support craft from the sea to an elevated position alongside the platform superstructure, means on the platform remotely operable from the craft for lowering a hydraulic line, connected to said hoisting apparatus, to the craft before it is raised from the sea, and connector means for connecting the lowered line to said hydraulic pressure source, such that the latter can supply hydraulic power to said hoisting apparatus.
Preferably the hoisting apparatus comprises a primary load-bearing line for connection to the craft, means operable for raising and lowering the primary line, a load member, a plurality of secondary lines connected to the load member, docking means on the load member for engagement with corresponding docking means on the support vessel, and means operable for raising and lowering the secondary lines independently on the load bearing line, said load member acting as a guide for the primary line.
A still further aspect of the invention provides a method of performing maintenance work on an unmanned offshore platform using a maintenance crew, wherein the crew:
(i) are transported in a sea-going support craft to the platform;
(ii) transfer from the craft, floating alongside the platform, to the platform superstructure;
(iii) connect a line connected to an operating device on the superstructure to a generator of power on the craft, for energising said operating device; and
(iv) perform said maintenance work, step (iii) being performed before, during or after step (ii).
With this method, the advantage is achieved that the operating device on the superstructure is powered by the generator on the support craft. Furthermore, the cost of providing a hoisting apparatus for raising and lowering the craft is avoided. However, the method would normally only be suitable for use in less hostile weather and sea conditions, where the craft can be moored alongside the platform.
The generator of power, the line and the operating device may all be hydraulic, or they may be electrical.